The present invention relates to an apparatus for processing substrates by subjecting at least part of the surface of the substrate to alternating surface reactions of two or more precursor materials. More particularly the present invention relates to an apparatus for processing substrates according to the principles of atomic layer deposition (ALD). In this application the term ALD means atomic layer epitaxy (ALE) and other similarly named methods realizing the principles of ALD. The atomic layer deposition apparatuses typically comprise a vacuum chamber inside which the substrates are processed. A separate reaction chamber may also be arranged inside the vacuum chamber such that the substrates are loaded into the reaction chamber and processed in the reaction chamber. The loading of the substrates may be carried out manually or by a loading device such as a loading robot. Conventionally the loading of the substrates into the ALD apparatus is carried out in normal ambient atmosphere, room atmosphere or atmosphere of a clean room. The present invention relates to the loading of the substrates into substrate holders for supporting said substrates.
WO 2009/144371 discloses an apparatus in which material is deposited on surfaces of a batch of vertically placed substrates in a reaction chamber. In the publication a batch of vertically placed substrates comprises a set of wafers placed in parallel into a movable substrate holder. The substrate holder is attached to a movable reaction chamber lid and the reaction chamber size is specially optimized for the size of the batch of vertically placed substrates or for the size of a substrate holder carrying the substrates. WO 2009/144371 discloses further that the spacing between the substrates is small for improving the efficiency of the reaction space but large enough to enable precursor flow to enter in between the substrates. The publication does not disclose how the substrates are loaded to the batch but because of the small spacing between the substrates in the batch increases requirements of the loading phase.
The common way to build a batch reactor is to use fixed shelves for the substrates as is used in the disclosure of the WO 2009/144371. One of the problems associated with the above mentioned prior art apparatus is that the loading device, for example an end-effector of a robot arm, must be very small because of the limited access. In order to get the substrates loaded to the substrate holder there needs to be space for the loading device to access between the shelves and to place the substrate there. The heavier the substrate is the more space is needed for the loading device to place the substrate to the shelf. At the same time cross section area becomes bigger resulting in a need for higher flows and correspondingly more piping and pumps. Another way to build a batch reactor is to arrange shelves such that the distance between following shelves is longer but this leads to other problems such as to more extensive precursor consumption, slower flushing and more extensive consumption of flushing gases and in conclusion to larger ALD apparatus. Some problems with the film quality may also arise when space between substrates becomes big. Problems may also arise with delivering enough precursors in conventional ways. When the size of the apparatus becomes larger there are also problems with transportation because of the height of the equipment.